Electromagnetic flowmeter production calibration method applicable to non-full-pipe states

Abstract

An electromagnetic flowmeter production calibration method applicable to non-full-pipe states. The method comprises: assuming that a total of n points are calibrated from low liquid levels to high liquid levels; setting the calibrated first point as a meter coefficient k1 at a liquid filling ratio H1; setting the calibrated second point as a meter coefficient k2 at a liquid filling ratio H2; continuing in this manner, setting the calibrated nth point as a meter coefficient kn at a liquid filling ratio Hn, wherein n is a natural integer, and both Hn and kn are specific values of actual-flow calibration; and setting the last calibrated point to be in a full-pipe state, i.e., using a calibration method for a meter coefficient k under full-pipe flow to implement metering in the full-pipe state. On the basis of the theory of a meter coefficient k changing along with a liquid level h in a non-full-pipe state and different liquid levels corresponding to unique k values, by means of performing actual-flow calibration and piecewise fitting on the k values at various liquid level points, the present invention realizes high-precision measurement in a full-pipe state and a non-full-pipe state while reducing the production calibration cost.

Description

A production calibration method of electromagnetic flowmeter for non-full pipe TECHNICAL FIELD

[0001] The present application belongs to the technical field of electromagnetic flow calibration, and particularly relates to a production calibration method of electromagnetic flowmeter for non-full pipe. BACKGROUND

[0002] With the accelerating pace of environmental governance and protection in China, the demand for effective measurement of sewage discharge is also increasing. Municipal drainage pipelines are usually non-full pipes, and may be in a full pipe state at a specific time. Sewage often contains a large amount of dry branches, rotten leaves and household garbage, etc. The commonly used ultrasonic and Doppler flowmeters need to be fixed at the bottom of the pipeline, which is easy to hang garbage, causing inaccurate data and pipeline blockage. The inner wall of the electromagnetic flowmeter is free of any protrusions, and there is no pressure loss, so the measurement accuracy is high and the stability is good. It is the most suitable flowmeter for long-term monitoring of municipal drainage pipelines.

[0003] In traditional applications, electromagnetic flowmeters are mainly used to measure the flow of full pipe fluid. Under the condition of full pipe, the weight function is constant as 1. According to Faraday's law of electromagnetic induction, the induced voltage signal generated by the sensor maintains a linear relationship with the average flow rate of the fluid. Therefore, the instrument coefficient of the sensor (i.e. the proportional coefficient between the induced voltage signal and the flow rate) remains constant, resulting in high measurement accuracy. The flow correction method for full pipe flow is usually an interval correction for flow or flow rate points.

[0004] However, in the case of non-full pipe flow, the change in the shape of the fluid cross section causes the weight function to no longer remain constant, but to be a function of the liquid level height, which makes the relationship between the induced voltage signal of the flowmeter and the average flow rate complex, not a simple linear relationship, and the instrument coefficient of the electromagnetic flowmeter will also change. This means that at different liquid levels, the same flow rate may produce different induced voltage signals. Therefore, the calibration method applied to full pipe flow will significantly decrease the measurement accuracy under the condition of non-full pipe flow, and the flow correction method for full pipe flow cannot be effectively applied to non-full pipe flow.

[0005] Current domestic patents on non-full pipe electromagnetic flowmeters can be roughly divided into two categories. The first category of patents uses special installation methods such as U-shaped pipes to ensure that the flowmeter is always in a full pipe state. However, this design scheme is prone to cause pipeline siltation and blockage problems. The second category of patents adjusts the position of the electrodes and combines with the liquid level meter to measure the liquid level, and uses the flow rate area method to calculate the flow. Although this scheme has some innovation in structure, it is still based on an assumption that the instrument coefficient is considered as a fixed value same as that in full pipe, so it is often difficult to achieve the expected accuracy in actual application.

[0006] In order to meet the requirement of accurately measuring the flow rate in full pipe and non-full pipe conditions, a new type of calibration method and algorithm need to be developed to accurately measure and effectively correct the fluid flow rate in non-full pipe condition, and ensure high-precision measurement results under different liquid level conditions. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a production calibration method of an electromagnetic flowmeter for non-full pipe, according to the theory that the instrument coefficient k changes with the liquid level h in non-full pipe condition, and different liquid levels correspond to a unique k value, the present application realizes high-precision measurement in full pipe and non-full pipe conditions by real flow calibration and segmented fitting of k values at each liquid level point, while reducing the production calibration cost.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is:

[0009] A production calibration method of an electromagnetic flowmeter for non-full pipe, assuming that the liquid level is calibrated at n points from low to high;

[0010] Let the first calibration point be the instrument coefficient k1 of the liquid level fullness H1; the second calibration point be the instrument coefficient k2 of the liquid level fullness H2; and so on, the nth calibration point be the instrument coefficient kn of the liquid level fullness Hn. n n ; wherein n is a positive integer, H n , k n are specific values of real flow calibration; the last calibration point is full pipe, that is, the calibration method of the instrument coefficient k when the full pipe flow is realized;

[0011] According to the calibration formula of the instrument coefficient k in non-full pipe, the specific values of the calibration coefficient k are obtained by real flow calibration of n-1 points in sequence.

[0012] Preferably, when the full pipe flow, the liquid level fullness H(h) is calculated as follows:

[0013] In the formula, h is the liquid level height in the flowmeter pipe, and D is the diameter of the flowmeter pipe.

[0014] Preferably, according to the calibration formula of the instrument coefficient k in non-full pipe, the specific values of the calibration coefficient k are obtained by real flow calibration of n-1 points in sequence, wherein the calibration formula of the instrument coefficient k in non-full pipe is:

[0015] In the formula, Q is the instantaneous flow rate of the standard meter, U is the flow rate signal or flow rate display value of the flowmeter, and A is the cross-sectional area of the liquid in the pipe;

[0016] The cross-sectional area function A(h) of the liquid in the pipe is as follows:​

[0017] wherein h is the liquid level height in the flowmeter pipe, and D is the diameter of the flowmeter pipe.

[0018] The real flow calibration is performed by using the segmented calibration method when the pipe is not full, including the following three ways:

[0019] The first way is to perform the real flow calibration by using the segmented calibration method when the pipe is not full, and the steps are as follows:

[0020] 1) A k-H scatter plot is established for the real flow calibration point data, and m linearly good intervals are determined, i.e. liquid fullness H = {X i |1≤i≤m≤n-1} m is a positive integer; wherein Xi represents the i-th linearly good H interval.

[0021] 2) The segmented linear fitting is performed on the calibration points in X m interval, and the corresponding fitting functions are g1(H) ~ g m (H);

[0022] 3) After the instrument coefficient k(H) function fitting is completed, the flowmeter measured pipe liquid level height h and flow velocity signal U are collected, and the pipe fluid flow velocity V and flow Q v can be calculated according to the flow velocity formula and the flow formula.

[0023] Preferably, the instrument coefficient k(H) expression in step 2) is:

[0024] ① k(H) = k1, H < H1;

[0025] ② k(H) = g i (H), H ∈ X i ;

[0026] ③ k(H) = k n , H ≥ H n ;

[0027] The second way is to perform the real flow calibration by using the segmented calibration method when the pipe is not full, and the steps are as follows:

[0028] 1) For the real flow calibration point data, the H is divided into n-1 adjacent point intervals by using the segmented linear interpolation method, i.e. liquid fullness H = {X j |1≤j≤n-1} X j = [H j , H j+1 ), j is a positive integer, and n ≥ 2; and the instrument coefficient k(H) expression two is as follows:

[0029] wherein j is a positive integer, j ∈ [1, n-1], and n ≥ 2;

[0030] 2) The second expression of the instrument coefficient k(H) is:

[0031] ① k(H) = k1, H < H1;

[0032] ②

[0033] ③ k(H) = k n , H ≥ H n .

[0034] 3) After the function fitting of the instrument coefficient k(H) is completed, the flow rate V and the flow Q of the fluid in the pipe can be calculated according to the flow rate formula and the flow formula by collecting the liquid level height h and the flow rate signal U measured by the flowmeter. v .

[0035] Method three: the segmented calibration method is used for real flow calibration when the pipe is not full, and the steps are as follows:

[0036] 1) For the real flow calibration point data, the cubic spline interpolation method divides H into n-1 adjacent point intervals, i.e. the liquid level fullness H = {X r |1 ≤ r ≤ n-1}, X r = [H r , H r+1 ), r is a positive integer, and n ≥ 4;

[0037] The calibration point positions of X1-X n-1 are calculated to obtain their cubic spline interpolation functions f1(H)-f n-1 (H), and the boundary condition is preferably the natural boundary condition.

[0038] 2) The third expression of the instrument coefficient k(H) is:

[0039] ① k(H) = k1, H < H1;

[0040] ② k(H) = f r (H), H ∈ [H r , H r+1 ];

[0041] ③ k(H) = k n , H ≥ H n .

[0042] 3) After the function fitting of the instrument coefficient k(H) is completed, the flow rate V and the flow Q of the fluid in the pipe can be calculated according to the flow rate formula and the flow formula by collecting the liquid level height h and the flow rate signal U measured by the flowmeter. v .

[0043] Preferably, the flow rate formula in step 3) is:

[0044] where V is the average flow velocity in the pipe, and U is the flow velocity signal.

[0045] Preferably, the flow rate formula in step 3) is:

[0046] Preferably, the derivation process of the flow velocity formula and the flow rate formula in step 3) is as follows:

[0047] In a closed circular pipe, the working conditions of water flow are usually divided into non-pressure non-full pipe flow and pressure full pipe flow. The volume flow rate is calculated by the flow velocity-area method, and the formula is: V Q = VA (1);

[0048] where Q is the instantaneous flow rate, V is the average flow velocity in the pipe, and A is the cross-sectional area of the liquid in the flowmeter pipe. V

[0049] In order to realize the measurement of non-full pipe flow, the average flow velocity V of the non-full pipe fluid in the flowmeter pipe is measured by the flow velocity sensor, and the liquid level h in the flowmeter pipe is measured by the liquid level sensor. According to formula (2), the cross-sectional area A of the liquid in the pipe can be calculated:

[0050] where D is the diameter of the flowmeter pipe, and h is the liquid level height in the flowmeter pipe.

[0051] According to Faraday's law of electromagnetic induction and J.A.Shercliff's weight function theory, the induced voltage measured on the electrodes is the collection of all flow elements in the cross section of the electrodes. If the magnetic field intensity on the flow element i is B i , the effective length of the flow element cutting the magnetic force line is l i , and the flow element velocity is v i , then the calculation formula (3) of the induced voltage on the measuring electrodes a and b is:

[0052] From formula (3), the calculation formula (4) of the average flow velocity V can be derived:

[0053] Define the fullness H of the liquid level in the flowmeter as formula (5):

[0054] For each specific liquid level height, there is a unique value of the weight function W, which is denoted as W(H); for each specific liquid level height, there is a unique value of the magnetic field intensity B, which is denoted as B(H); then there is a function k(H) that satisfies formula (6), that is, the instrument coefficient k is only related to the liquid level fullness H:

[0055] ​Substitute formula (5) and formula (6) into formula (4) to obtain the flow rate V calculation formula about the sensor measured U and H:

[0056] Substitute formula (7) and formula (2) into formula (1) to obtain the flow Q calculation formula about the sensor measured U and h V The calculation formula is:

[0057] A production calibration system for a non-full pipe electromagnetic flowmeter adopts a production calibration method for a non-full pipe electromagnetic flowmeter.

[0058] The present application can achieve the following beneficial effects:

[0059] (1) High-precision measurement: By calibrating the liquid level fullness, it can be applied to high-precision measurement in non-full pipe and full pipe conditions, meeting the changing actual application scenarios.

[0060] (2) Cost optimization: The segmented calibration scheme reduces the number of calibrations by analyzing key liquid level points, effectively reducing calibration and production costs.

[0061] (3) Wide applicability: The flow rate electrode structure and position requirements are not high, and the existing products can be directly modified, improving the applicability.

[0062] (4) Clean and environmentally friendly: No pressure loss, and the measurement accuracy is not affected by the physical properties of the fluid, especially suitable for sewage measurement.

[0063] (5) Reduce maintenance: There are no protrusions on the inner wall, reducing pipe blockage and instrument maintenance problems.

[0064] (6) Promote environmental monitoring: Adapt to environmental governance needs and provide an effective tool for pollutant emission monitoring.

[0065] (7) Versatility: Not limited to municipal drainage, but also applicable to industrial wastewater treatment and other flow measurement scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0066] The present application will be further described below in conjunction with the drawings and examples:

[0067] Fig. 1 is a flowmeter 1 instrument coefficient curve changing with liquid level fullness H under experimental verification of the present application;

[0068] Fig. 2 is a flowmeter 2 instrument coefficient curve changing with liquid level fullness H under experimental verification of the present application;

[0069] Fig. 3 is a flow error line graph in Example 1 of the present application;

[0070] Fig. 4 is a flow error line graph in Example 2 of the present application. DETAILED DESCRIPTION

[0071] The preferred scheme is shown in Figs. 1-4. A method for producing and calibrating an electromagnetic flowmeter for non-full pipe, 1, assumes that the liquid level is calibrated from low to high for n points;

[0072] 2, the first calibration point is the instrument constant k1 when the liquid level is fullness H1; the second calibration point is the instrument constant k2 when the liquid level is fullness H2; and so on, the nth calibration point is the instrument constant kn when the liquid level is fullness Hn. n n ; Wherein, n is a positive integer, H n , k n are specific values of real flow calibration; the last calibration point is full pipe, that is, the calibration method of instrument constant k when the flow is full pipe, to realize the measurement when the flow is full pipe.

[0073] Wherein, the liquid level fullness H(h) is calculated as follows:

[0074] In the formula, h is the liquid level height in the flowmeter pipe, and D is the diameter of the flowmeter pipe.

[0075] 3, according to the calibration formula of instrument constant k when the flow is non-full pipe, sequentially calibrate n points to obtain the specific value of calibration constant k, wherein the calibration formula of instrument constant k when the flow is non-full pipe is:

[0076] In the formula, Q is the instantaneous flow of the standard meter, U is the flow rate signal or flow rate display value of the flowmeter, and A is the cross-sectional area of the liquid in the pipe.

[0077] The cross-sectional area function A(h) of the liquid in the pipe is as follows:

[0078] The method for segment calibration is as follows:

[0079] 1) When segment calibration is performed, a k-H scatter plot is established for real flow calibration point data, and the m intervals with good linearity are determined, that is, the liquid level fullness H={X i |1≤i≤m≤n-1} m is a positive integer;

[0080] 2) Segment linear fitting is performed on the calibration points in the X1-X m intervals, and the corresponding fitting functions are g1(H)-g m (H), respectively. The expression of instrument constant k(H) is as follows:

[0081] ① k(H)=k1, H

[0082] ② k(H)=g i ​(H), H∈X i ;

[0083] ③k(H)=k n H≥H n ;

[0084] 3) After the instrument coefficient k(H) function is fitted, by collecting the liquid level height h and flow velocity signal U measured by the flow meter in the pipe, the fluid velocity V and flow rate Q in the pipe can be calculated according to the flow velocity formula and the flow rate formula. v :in:

[0085] Flow rate formula:

[0086] Flow formula:

[0087] As an alternative, in actual production, prototypes of the same model and specifications produced by the same manufacturer maintain basic consistency in geometric dimensions and instrument parameters. Although their instrument coefficient values ​​may differ to some extent, they exhibit similar patterns of change. Therefore, actual flow calibration can be performed only at key liquid level heights, thereby reducing the number of calibration points.

[0088] To further reduce the number of calibration points and calibration costs, the instrument coefficient k(H) expression in step 3) can be replaced with the simplified expression for the instrument coefficient k(H) based on piecewise linear interpolation:

[0089] For actual flow calibration point data, the piecewise linear interpolation method divides H into n-1 adjacent point intervals, i.e., the liquid level filling degree H = {X} j |1≤j≤n-1},X j =[H j H j+1 ), where j is a positive integer and n≥2. The expression for the instrument coefficient k(H) is as follows:

[0090] ①k(H)=k1,H

[0091] ②

[0092] ③k(H)=k n H≥H n .

[0093] As an alternative, to improve the smoothness and continuity of the instrument coefficient calibration curve and ensure a smooth transition of the instrument coefficient across different intervals, the instrument coefficient k(H) expression in step 3) can be replaced with: a smooth and continuous instrument coefficient k(H) expression based on cubic spline interpolation.

[0094] ​For real flow calibration point position data, cubic spline interpolation method divides H into n-1 adjacent point position intervals, i.e. r |1≤r≤n-1},X r =[H r ,H r+1 ),r is a positive integer, and n≥4.

[0095] The calibration point positions in X1-X n-1 interval are respectively obtained, and the cubic spline interpolation functions f1(H)-f n-1 (H) are respectively obtained.

[0096] ①k(H)=k1, H<H1;

[0097] ②k(H)=f r (H), H∈[H r ,H r+1 );

[0098] ③k(H)=k n , H≥H n ;

[0099] The segmented calibration method provided by the application has the following formula derivation process:

[0100] In a closed circular pipeline, the working conditions of water flow are usually divided into non-pressure non-full pipe flow and pressure full pipe flow, and the flow rate-area method is usually used to calculate the instantaneous flow rate, and the flowmeter must have the ability to measure the flow rate and liquid level simultaneously, and the formula is: Q V =VA (1).

[0101] In the formula, Q V is the instantaneous flow rate, V is the average flow rate in the pipe, and A is the liquid cross-sectional area in the flowmeter pipe.

[0102] In order to measure the non-full pipe flow, the average flow rate V of the non-full pipe fluid in the flowmeter pipe is measured by the flow rate sensor, the liquid height h in the flowmeter pipe is measured by the liquid level sensor, and the liquid cross-sectional area A in the pipe can be calculated according to formula (2):

[0103] In the formula, D is the diameter of the flowmeter pipe, and h is the liquid level height in the flowmeter pipe.

[0104] The working principle of electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. When the conductive fluid passes through the pipeline with a pair of measuring electrodes with a distance of L at a flow rate V, the pair of electrodes will generate an induced electromotive force E = BLV perpendicular to the direction of the magnetic field and the direction of the liquid flow. According to the J. A. Shercliff weight function theory, the induced voltage measured on the measuring electrode is the collection of all flow elements in the electrode section. The weight function W represents the contribution of the electric potential generated by each point in the effective area to the flow rate signal between the electrodes, reflecting the attenuation coefficient caused by the geometric position. If the magnetic field intensity of flow element i is B i , the effective length of flow element cutting magnetic force line is l i , and the flow element velocity is v i , the induced voltage on the measuring electrodes a and b is shown in formula (3).

[0105] From formula (3), the calculation formula (4) of the average flow rate V can be derived.

[0106] The formula (5) of the liquid level fullness H in the flowmeter is defined.

[0107] The weight function W is a spatial function related to the size, geometry (including electrodes), and liquid fullness in the pipe. Under the condition that the hardware parameters of the sensor remain unchanged, the weight function W is only related to the liquid level. Some scholars have calculated the weight function value under different fullness by finite element numerical analysis method, and proved that the weight function W will change with the liquid level. Therefore, the functional relationship between the weight function W and the liquid level fullness H can be expressed as W(H).

[0108] The magnetic field generated by the excitation coil is proportional to the excitation current and the magnetic permeability of the medium. The magnetic permeability of different media will affect the propagation of the magnetic field. The magnetic permeability of air and water is not the same. When the pipe is not full, the magnetic field distribution will pass through the upper air gap and the lower water, and the size of the air gap area changes with the liquid level in the pipe, resulting in that the magnetic field distribution is not constant, but changes with the liquid level. Therefore, the functional relationship between the magnetic field intensity B and the liquid level fullness H can be expressed as B(H).

[0109] As mentioned above, there is a function relationship k(H) that satisfies formula (6), that is, the instrument coefficient k is only related to the liquid level fullness H. In practical applications, due to the influence of various factors such as manufacturing process, it is impossible to obtain a completely uniform magnetic field, and the data of weight function W and magnetic field intensity B cannot be accurately obtained. Therefore, the actual flow is usually calibrated to determine the approximate value of the instrument coefficient k.

[0110] Substituting equation (5) and equation (6) into equation (4) gives the flow rate V calculation formula about the sensor measured U and H:

[0111] Substituting equation (7) and equation (2) into equation (1) gives the flow rate Q calculation formula about the sensor measured U and h V Calculation formula:

[0112] Experimental verification

[0113] In this study, two electromagnetic flowmeters from different manufacturers were used for experimental verification, and the verification content was that each liquid level fullness H had a unique instrument coefficient k. Due to the non-full pipe state, it was difficult to control the liquid level height to conduct multiple experiments for a certain liquid level value in the calibration experiment, therefore, the experiment was conducted in a high-to-low manner according to a certain flow difference value, the standard table flow of the full pipe section was converted by collecting the pulse output quantity within 1 minute, 2-3 times of data were collected at each point to obtain the average value, and the experimental process was repeated multiple times to verify the repeatability.

[0114] In flowmeter 1, there were 3 pairs of flow rate electrodes distributed at 30%, 20%, and 10% of the flowmeter inner diameter height, the flowmeter pipe inner diameter was 376mm, and the experimental flow range was 35-365m 3 / h, and the water quality was sewage mixed with slurry, the experiment was carried out in the flow laboratory of Chongqing Three Gorges Ecological Environment Technology Innovation Center Co., Ltd. During the experiment, due to the large deviation between the front and rear straight pipe sections and the flowmeter inner diameter, the liquid level fluctuated greatly, therefore, the front and rear straight pipe sections were replaced in February 2024. By changing the standard flow and the pipe slope value i (unit: percentage %), and measuring multiple times on different dates, the obtained instrument coefficient changed with the liquid level fullness H as shown in Figure 1, and the instrument coefficient was not normalized.

[0115] In flowmeter 2, the flow rate electrodes were distributed at 10% of the flowmeter inner diameter height, the flowmeter pipe inner diameter was 300mm, and the flow range was 14-314m 3 / h, and the water quality was clear water, the experiment was carried out on the non-full pipe real flow calibration device of Qingtian Weiyige Intelligent Instrument Technology Park. The experiment started to correct the instrument coefficient at the point of H = 76%, and the indicated flow error of this point was 0. By changing the standard flow, the experimental process was repeated 2 times to verify the repeatability, and the measured instrument coefficient changed with the liquid level fullness H as shown in Figure 2.

[0116] The experimental data of flowmeter 2 are shown in Table 1, the standard flow Q (m 3h) measured by standard table of full pipe section; flow velocity U (m / s) is flow velocity data measured by sensor; liquid level height h is measured by ultrasonic liquid level meter of flow meter, and liquid level ratio H is obtained by conversion of H = h / D; cross-sectional area A (m 2 ) is obtained by calculation of cross-sectional area formula; instrument coefficient k is obtained by calculation of k = Q / (U*A).

[0117] Table 1

[0118] The experimental verification results of the two different manufacturers' electromagnetic flowmeters can be concluded as follows:

[0119] A. Under the non-full pipe state, the instrument coefficient k changes with the liquid level fullness H, and has a unique value, and the two are nonlinear;

[0120] B. The instrument coefficient k is independent of the pipe slope;

[0121] C. The instrument coefficients of flow velocity electrodes at different positions are not the same, and when H is not more than 50%, the higher the flow velocity electrode position, the smaller the instrument coefficient value.

[0122] D. The instrument coefficient k of the flowmeter with different parameters does not have the same trend with the change of liquid level fullness H.

[0123] Example 1:

[0124] By analyzing the k-H scatter plot in FIG. 2, it is found that K presents a good linear relationship in two intervals H∈(13.67%, 22.5%) and (22.5%, 77.17%), so it is divided into corresponding two intervals for linear fitting, and the fitting formula is g1 = 1.207*H + 0.797 and g2 = -0.1115*H + 1.0848, then the instrument coefficient k(H) expression is as follows:

[0125] a. k(H) = 0.95505, H < 13.67%;

[0126] b. k(H) = 1.207*H + 0.797, H∈[13.67%, 22.5%);

[0127] c. k(H) = -0.1115*H + 1.0848, H∈[22.5%, 77.17%);

[0128] d. k(H) = 0.98749, H≥77.17%;

[0129] Substitute the above k(H) expression into the flow Q VThe calculation formula is used to calculate the flow error of the standard table, and the flow error of the standard table is error 1; the flow error of the standard table is error 0 (only correct the instrument coefficient at 76% liquid level to make the indicated flow error 0), and the calibration method can better improve the measurement accuracy under the non-full pipe state.

[0130] Example 2:

[0131] By analyzing the k-H scatter plot in FIG. 2, it can be considered that the key point of the flowmeter is H∈{13.67%, 22.5%, 77.17%} three points, and the products of the same batch have similar variation rules, in order to further reduce the number of calibration points and calibration cost, the instrument coefficient k(H) expression one in step 3) is replaced by the following formula:

[0132] a.k(H)=0.95505,H<13.67%;

[0133] b.k(H)=0.95505+(H-0.1367)*1.2016,H∈[13.67%,22.5%);

[0134] c.k(H)=1.0612-(H-0.225)*0.1348,H∈[22.5%,77.17%);

[0135] d.k(H)=0.98749,H≥77.17%;

[0136] The above k(H) expression is substituted into the flow Q V The calculation formula is used to calculate the flow error of the standard table, and the flow error of the standard table is error 1; the flow error of the standard table is error 0 (only correct the instrument coefficient at 76% liquid level to make the indicated flow error 0), and the calibration method can better improve the measurement accuracy under the non-full pipe state.

[0137] The above-mentioned embodiments are only preferred technical solutions of the present application, and should not be regarded as limiting the present application, and the protection scope of the present application should be the technical solutions recited in the claims, including the equivalent replacement solutions of the technical features recited in the claims. That is, within this range, equivalent replacement improvements are also within the protection scope of the present application.

Claims

1. A method for calibrating electromagnetic flowmeters used in non-full-pipe applications, characterized in that: Assume that the liquid level is calibrated at n points from low to high; Let the instrument coefficient k1 be the first calibrated point, representing the liquid level fill degree H1; let the instrument coefficient k2 be the second calibrated point, representing the liquid level fill degree H2; and so on, calibrating the nth point as the liquid level fill degree H... n Instrument coefficient k at time n Where n is a positive integer, H n k n All values ​​are specific values ​​calibrated for actual flow; the last calibration point is for a full pipe, that is, the calibration method of the instrument coefficient k is adopted when the pipe is full to achieve measurement when the pipe is full. According to the calibration formula of the instrument coefficient k when the pipe is not full, the actual flow calibration is performed at n-1 points in sequence to obtain the specific value of the calibration coefficient k. According to the calibration formula of the instrument coefficient k when the pipe is not full, the actual flow calibration is performed on n-1 points in sequence to obtain the specific value of the calibration coefficient k. The calibration formula of the instrument coefficient k when the pipe is not full is as follows: In the formula: Q is the instantaneous flow rate of the standard meter, U is the flow rate signal or flow rate display value of the flow meter, and A is the cross-sectional area of ​​the liquid in the pipe; The cross-sectional area function A(h) of the liquid inside the pipe is as follows: In the formula, h is the liquid level height inside the flow meter tube, and D is the inner diameter of the flow meter tube; When the pipe is not full, a segmented calibration method is used for actual flow calibration, and the steps are as follows: 1) Establish a kH scatter plot based on the actual flow calibration point data, and determine the H interval with good linearity for m segments, i.e., the liquid level filling degree H = {Xi|1≤i≤m≤n-1}, where m is a positive integer, and X i This represents the H interval with relatively good linearity; 2) For X1 to X respectively m Piecewise linear fitting is performed on the calibration points within the interval, and the corresponding fitting functions are g1(H)~g m (H); 3) After the instrument coefficient k(H) function is fitted, by collecting the liquid level height h and flow velocity signal U measured by the flow meter in the pipe, the fluid velocity V and flow rate Q in the pipe can be calculated according to the flow velocity formula and the flow rate formula. v ; The expression for the instrument coefficient k(H) in step 2) is: ①k(H)=k1,H<H1; ②k(H)=g i (H),H∈X i ; ③k(H)=k n ,H≥H n ; When the pipe is not full, a segmented calibration method is used for actual flow calibration, and the steps are as follows: 1) For actual flow calibration point data, the piecewise linear interpolation method divides H into n-1 adjacent point intervals, i.e., the liquid level filling degree H = {X} j |1≤j≤n-1},X j =[H j H j+1 ), where j is a positive integer, n≥2; the expression for the instrument coefficient k(H) is as follows: Where j is a positive integer, and j∈[1, n-1], n≥2; 2) The second expression for the instrument coefficient k(H) is: ①k(H)=k1,H<H1; ② ③k(H)=k n ,H≥H n ; 3) After the instrument coefficient k(H) function is fitted, by collecting the liquid level height h and flow velocity signal U measured by the flow meter in the pipe, the fluid velocity V and flow rate Q in the pipe can be calculated according to the flow velocity formula and the flow rate formula. v .

2. The method for calibrating an electromagnetic flowmeter for use in non-full pipe applications according to claim 1, characterized in that: When the pipe is fully filled, the formula for calculating the degree of filling H(h) is as follows: In the formula, h is the liquid level height inside the flow meter tube, and D is the inner diameter of the flow meter tube.

3. The method for calibrating an electromagnetic flowmeter for use in non-full pipe applications according to claim 1, characterized in that: When the pipe is not full, a segmented calibration method is used for actual flow calibration, and the steps are as follows: 1) For actual flow calibration point data, the cubic spline interpolation method divides H into n-1 adjacent point intervals, i.e., the liquid level filling degree H = {X} r |1≤r≤n-1},X r =[H r H r+1 r is a positive integer, n≥4; For X1 to X n-1 The calibration points of the interval are used to obtain their cubic spline interpolation functions f1(H) to f2(H). n-1 (H), the boundary conditions are natural boundary conditions. 2) The third expression for the instrument coefficient k(H) is: ①k(H)=k1,H<H1; ②k(H)=f r (H),H∈[H r ,H r+1 ); ③k(H)=k n ,H≥H n ; 3) After the instrument coefficient k(H) function is fitted, by collecting the liquid level height h and flow velocity signal U measured by the flow meter in the pipe, the fluid velocity V and flow rate Q in the pipe can be calculated according to the flow velocity formula and the flow rate formula. v .

4. The method for manufacturing and calibrating an electromagnetic flowmeter that can be used in a non-full pipe, as described in claim 3, is characterized in that: The flow velocity formula in step 3) is: In the formula, V is the average flow velocity inside the pipe, and U is the flow velocity signal.

5. A method for calibrating an electromagnetic flowmeter for use in non-full pipe applications according to claim 4, characterized in that: The flow rate formula in step 3) is:

6. The method for calibrating an electromagnetic flowmeter for use in non-full pipe applications according to claim 5, characterized in that: The derivation process of the velocity formula and flow rate formula in step 3) is as follows: In a closed circular pipe, the flow conditions are typically divided into unpressurized non-full pipe flow and pressurized full pipe flow. The volumetric flow rate is calculated using the velocity-area method, with the following formula: Q V =AND (1); In the formula, Q V V is the instantaneous flow rate, V is the average flow velocity in the pipe, and A is the cross-sectional area of ​​the liquid in the flow meter pipe. To measure the flow rate of a partially filled pipe, the average flow velocity V of the fluid in the partially filled pipe is measured by a flow velocity sensor, and the liquid height h in the pipe is measured by a liquid level sensor. The cross-sectional area A of the liquid in the pipe can be calculated according to equation (2): In the formula, D is the inner diameter of the flow meter tube, and h is the liquid level height inside the flow meter tube; According to Faraday's law of electromagnetic induction and Jashercliff's weighting function theory, the induced voltage measured on the measuring electrode is the collection of all current elements within the electrode cross-section. Let the magnetic field strength on current element i be B. i The effective length of the flow element cutting the magnetic field lines is l i The velocity of the flow element is v i Then, the formula (3) for calculating the induced voltage on measuring electrodes a and b is: From equation (3), the formula (4) for calculating the average flow velocity V can be derived: Define the formula for the degree of liquid filling H in the flow meter (5): For each specific liquid level height, there exists a uniquely determined weighting function W, denoted as W(H); for each specific liquid level height, there exists a uniquely determined magnetic field strength B, denoted as B(H); then there exists a function k(H) satisfying formula (6), that is, the instrument coefficient k is only related to the liquid level filling degree H: Substituting equations (5) and (6) into equation (4), we obtain the formula for calculating the flow velocity V of the measured values ​​U and H: Substituting equations (7) and (2) into equation (1) yields the flow rate Q for the measured values ​​of U and h by the sensor. V Calculation formula:

7. A calibration system for electromagnetic flowmeters used in non-full-pipe applications, characterized in that: The method for production calibration of electromagnetic flowmeters that can be used in non-full pipes, as described in claim 6, was adopted.

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